The related applications describe a cleaning solvent for aerospace applications that is essentially nontoxic, nonflammable, and nonvolatile. Preferably being a eutectic mixture of ethylene carbonate and an alkylene diester (particularly ethylene diacetate), this solvent is an effective replacement for methyl ethyl ketone (M.E.K.), a substance that is a powerful cleaning solvent but that is now restricted (or is likely to be restricted) and limited in its use because of toxicity or for environmental concerns.
Mixtures of ethylene carbonate (i.e. carbonate) and an alkyl diester, however, are susceptible of separation of the carbonate through crystallization of the ethylene carbonate upon cooling. Separation changes the characteristics of the solvent, and makes it difficult to handle. The separation can be overcome by preparing the mixture properly with the method of present invention, which stabilizes the mixture even to temperatures as low as at least about 32.degree. F. (0.degree. C.).